T-die and method of manufacturing the same

ABSTRACT

On at least the edge portion ( 9   e ) of the lip portion ( 9 ) of a T-die ( 1 ), a cladding layer ( 10 ) is provided. The cladding layer is formed by laser build-up welding to a base material with a powder of a corrosion resistant and wear resistant alloy comprising a nickel-based alloy or a cobalt-based alloy. The cladding layer has a metallographic structure in which metal borides are dispersed in a binder phase. The lip portion has high quality and has high durability. The manufacturing costs of the T-die can also be kept relatively low.

TECHNICAL FIELD

The present invention relates to a T-die having a slit-shaped dischargeport used for forming a film or a sheet comprising a resin material, anda manufacturing method thereof.

BACKGROUND ART

One of methods for manufacturing a resin film extrudes a molten resin byusing a die having a slit-shaped orifice (discharge port) referred to asa T-die. In particular, resin films for optical use are required to havehigh uniformity in film thickness and to be free of die lines(longitudinal streaks in an extrusion direction). Accordingly, it isrequired for a T-die used in this application as follows: the inner wallsurface of a molten resin flow channel inside the T-die is smooth andhas less friction with a molten resin; a lip portion at the tip end ofan orifice has a high dimensional accuracy and has a sharp edge; and theT-die has high durability to maintain the aforementioned conditions fora long time. So far, in correspondence to the requirements, a coatinglayer such as a hard chromium plating layer has been provided to amolten resin flow channel and a harder hard coating layer has beenprovided at a lip portion.

Patent Document 1 describes to provide a WC-based coating layer onto alip portion by means of flame spraying, the WC-based coating layercomprising an alloy formed by mixing WC particles as hard particles andNi, Co, or Cr as a binder. A hard chromium plating layer is provided tothe inner wall surface of a molten resin flow channel at portions otherthan the lip portion. However, since such a coating layer is relativelybrittle, the layer tends to suffer from a defect such as peeling,cracking, or chipping upon finishing the edge portion by grinding andpolishing after flame spraying. Such defect causes die lines to occur.Further, since adhesion between the WC-based coating layer and the hardchromium plating layer is not so satisfactory, peeling or cracking maypossibly be caused between the two layers.

Patent Document 2 describes a T-die formed by bonding, to a main body,tabular lip member comprising a super hard alloy by means of a ceramictype adhesive. According to this constitution, a lip edge can befinished into a sharp edge. However, the super hard alloy has inferioradhesion with a hard chromium plating layer. Besides, it is difficult toapply plating finish to a portion other than the lip portion due topresence of the adhesion portion. Further, ensuring a sufficientadhesion strength requires a large adhesion area by enlarging the superhard alloy portion. However, this increases the material cost.

Patent Documents 3 and 4 each describe a method of forming a lip portionby bonding a corrosion resistant and wear resistant alloy powder throughsintering and simultaneous diffusion bonding by Hot Isostatic Process(HIP) to a die main body comprising an austenite/ferrite double phasestainless steel alloy. A B (boron)-containing Ni-based alloy orcobalt-based alloy is used as the corrosion resistant and wear resistantalloy. A hard chromium plating layer is disposed to the inner wallsurface of a molten resin flow channel at portions other than the lipportion. Since the lip portion obtained by the method described in thePatent Documents 3 and 4 has a dense metallographic structure with lessdefects, the edge portion can be formed into a sharp edge at highaccuracy. However, an extremely complicated, expensive, and large-scaledmanufacturing equipment is required for practicing the method describedin the Patent Documents 3 and 4. Further, since the die main body in theHIP process is exposed to high temperature and high pressure, forexample, at 1300° C. and 130 MPa, the die main body is distorted andbent. In this case, it is necessary to apply fabrication to the die mainbody including allowance therefor (particularly, refer to PatentDocument 3). Thus, the method described in the Patent Documents 3 and 4involves a problem of requiring enormous amount of labors and costs.

PRIOR ART DOCUMENTS Patent Documents

PATENT DOCUMENT 1: JP-A-2006-224462

PATENT DOCUMENT 2: JP-A-2007-196630

PATENT DOCUMENT 3: JP-A-2012-20434

PATENT DOCUMENT 4: JP-A-2011-235500

SUMMARY OF THE INVENTION Problem to be Solved by the Invention

The present invention provides a T-die in which a lip portion has highquality and high durability, and which can be manufactured at arelatively low cost, and a manufacturing method thereof.

Means for Solving the Problem

The present invention provides a T-die comprising die main body providedtherein with a fluid material flow channel and having a lip portion thatforms a slit-shaped discharge portion at the tip end of the fluidmaterial flow channel. The lip portion includes a cladding layer formedat least an edge portion thereof, the cladding layer being formed bylaser build-up welding to a base material with a powder of a corrosionresistant and wear resistant alloy comprising a nickel-based alloy or acobalt-based alloy. In a preferred embodiment, the cladding layer has ametallographic structure in which metal borides or metal carbides aredispersed in a binder phase.

In a preferred embodiment of the T-die, a plating layer is disposed onthe inner wall surface of the fluid material flow channel in continuitywith the cladding layer. The present invention also provides a method ofmanufacturing the T-die having such a plating layer. The manufacturingmethod includes: a step of providing a material having a first surfacethat is a lip mating face, a second surface that is a lip end face, anda third surface that connects the first surface and the second surfaceand is inclined thereto; a step of forming a cladding layer by laserbuild-up welding over the third surface with a powder of a corrosionresistant and wear resistant alloy; a step of subsequently grinding thefirst surface and the second surface of the material together withportions of the cladding layer adjacent to the first surface and thesecond surface; a step of subsequently forming a plating layer over thesurface of the cladding layer and over the first surface of thematerial; and a step of subsequently grinding the plating layer suchthat the cladding layer is exposed and the cladding layer has a surfaceflush with the surface of the plating layer lying over the first surfaceof the material.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a longitudinal cross sectional view of a T-die according to anembodiment of the present invention in which (a) is an entire view and(b) is a diagram showing the vicinity of a lip edge shown in (a) at anenlarged scale.

FIG. 2 is a side elevational view showing an inner wall surface of a diemain body of the T-die shown in FIG. 1.

FIG. 3 is a diagram showing a method of manufacturing the T-die shown inFIG. 1.

FIG. 4 is a diagram showing laser build-up welding for forming acladding layer.

FIG. 5 is a copy of a microscopic photograph of a cladding layer formedby laser build-up welding.

FIG. 6A is a graph showing a hardness distribution of a layer formed bylaser build-up welding.

FIG. 6B is a graph showing a hardness distribution of a layer formed byHIP.

EMBODIMENTS FOR CARRYING OUT THE INVENTION

A preferred embodiment of the invention is to be described withreference to the appended drawings.

As shown in FIG. 1 and FIG. 2, a T-die 1 has a die main body 2comprising a pair of die members 3, 4. A molten resin flow channel(fluid material flow channel) 5 is formed between the die members 3 and4. The molten resin flow channel 5 has a charge portion 6, a manifoldportion 7, and a slit shape discharge portion 8 orderly from theupstream. The charge portion 6 at the longitudinal central portion ofthe T-die 1 is connected to a not illustrated extruder and a moltenresin is supplied from the charge portion 6 into the molten resin flowchannel 5. The supplied molten resin flows into the manifold portion 7of a substantially circular cross section extending in the longitudinaldirection of the T-die 1, spreads in the longitudinal direction of theT-die 1, then flows into the slit shape discharge portion 8, and isextruded in the form of a film from the opening end edge of thedischarge portion 8 onto a not-illustrated roller. A portion near theopen end edge of the discharge portion 8 of each of the die members 3and 4 is referred to as a lip portion 9. In FIG. 2, references 6 a, 7 a,and 8 a show wall surfaces of the die member 3 (4) facing the chargeportion 6, the manifold portion 7, and the discharge portion 8respectively. As is well-known to a person skilled in the art, theextrusion molding machine is formed by an extruder main body (notillustrated) that melts and extrudes a powdery or granular resinmaterial, the T-die attached to the discharge port of the extruder mainbody, and a roller (not shown) that receives a film-like resin extrudedfrom a T-die.

The lip portion 9 of the T-die 1 is formed of a cladding layer 10 formedby bonding an alloy powder of good corrosion resistance and wearresistance by powder laser build-up welding to the die members 3, 4 as abase material. The cladding layer 10 is depicted by a satin pattern ineach of the drawings. A plating layer 20 is formed to the surface (innerwall surface) of the die members 3, 4 facing the molten resin flowchannel 5. The plating layer 20 is formed also at the lower surface ofthe die members 3 and 4 in continuity with the lip portion 9. As clearlyshown particularly in FIG. 1( b), the plating layer 20 is disposed incontinuity with the cladding layer 10.

It is preferred that the plating layer 20 has low friction resistance tothe molten resin and has such wear resistance as not to be worn easilyeven when exposed to the flow of the molten resin. Further, where acorrosive gas evolves from the molten resin, the plating layer 20preferably has such a corrosion resistance as not corroded easily by thecorrosive gas. Specifically, the plating layer 20 can be formed of ahard chromium plating layer. Any plating layer 20 may be used so long asit has the properties described above and, for example, may also be anelectroless nickel plating layer.

The material forming the cladding layer 10 is preferably a powdercomprising a nickel-based alloy or a cobalt-based alloy. Most ofnickel-based alloys or cobalt-based alloy are often excellent in thecorrosion resistance and the wear resistance, thus suitable to the useof resin molding. The nickel-based alloy or the cobalt-based alloy hasexcellent bonding strength with iron and steel materials that can beused suitably as the material for the die main body and is suitable as aclad welding material. Nickel-based alloys or cobalt-based alloys ofvarious compositions are commercially available and suitable one can beselected in accordance with properties that are considered important(for example, wear resistance, corrosion resistance, easy formability tosharp edge, toughness, and bondability to the die main body). Inparticular, a nickel-based alloy or a cobalt-based alloy with additionof B (boron) or C (carbon) shows a metallographic structure in which a Bcompound or a C compound is dispersed in a binder phase and,accordingly, the alloy has high strength and is excellent in the wearresistance. Generally, a material of higher hardness can form the edgeportion having higher sharpness (sharp edge) compared with the materialnot having high hardness. Thus, also in this respect, the material ofhigher hardness is suitable as a material for the lip portion of theT-die.

Suitable compositions of the nickel-based alloy powder as the materialof the cladding layer 10 are shown by the following four examples:

(Ni alloy-1) 71.65 wt % Ni, 20.0 wt % Mo, 3.1 wt % B, 5.2 wt % Si, and0.05 wt % C;

(Ni alloy-2) 65.92 wt % Ni, 20.5 wt % Mo, 5.0 wt % Cu, 3.3 wt % B, 4.7wt % Si, and 0.08 wt % C;

(Ni alloy-3) 54.14 wt % Ni, 22.5 wt % Mo, 9.5 wt % W, 5.0 wt % Cu, 2.8wt % B, 5.4 wt % Si, and 0.66 wt % C; and

(Ni alloy-4) 57.0 wt % Ni, 16.5 wt % Cr, 17.0 wt % Mo, 5.0 wt % Fe, and4.5 wt % W.

Suitable compositions for the cobalt-based alloy powder are shown belowby the following two examples:

(Co alloy-1) 68.5 wt % Co, 20.0 wt % Cr, 5.1 wt % W, 1.5 wt % Ni, 3.1 wt% B, and 1.8 wt % Si; and

(Co alloy-2) 46.0 wt % Co, 30.0 wt % Cr, 2.5 wt % C, 1.0 wt % Si, 1.0 wt% Mn, 1.0 wt % Mo, 3.0 wt % Fe, 3.0 wt % Ni, and 12.5 wt % W.

By using the nickel-based alloy powder or the cobalt-based alloy powderhaving the composition described above, a cladding layer 10 having ahardness of 460 to 900 Hv can be obtained.

As shown in FIG. 1( b), a preferred dimension of the cladding layer 10is, for example, such that a cladding layer width W1 on the side of thelip mating face is 0.2 to 1.7 mm, and a cladding layer width W2 on theside of the lip end face from the edge is 0.2 to 2.4 mm. A suitableembodiment is, for example, such that the cladding layer width W1 on thelip mating face side is 1.2 mm, the cladding layer width W2 on the lipend face side is 2.1 mm, and an entire length of the lip portion 9 is1100 mm. In FIG. 1( b) and FIG. 3, the thickness of the plating layer 20is expressed rather thick in order to make the drawings easy to see.However, the thickness of the plating layer 20 is actually less than 100μm, for example, several tens μm in the final product, which isconsiderably smaller than the thickness of the cladding layer 10.

The reason for setting the dimension of the cladding layer 10 as aboveis described below.

Only considering the performance of the T-die 1, it may suffice thatonly the edge portion 9 e of the lip portion 9 which undergoes thelargest burden is formed of the cladding layer 10 and other portion thanthe edge portion 9 e in contact with the molten resin can be formed ofthe plating layer 20 (hard chromium plating layer, electroless platinglayer, or the like) that can be formed at a reduced cost than that forthe cladding layer 10 with no problem at all. Since the material for thecladding layer 10 is extremely expensive, it is not preferred to makethe dimension of the cladding layer 10 so large with a view point ofreducing the cost.

However, when a defect, for example, chipping is caused to the lipportion 9 (particularly edge portion 9 e), since the defect can berepaired by grinding or polishing, it is preferred that the dimension ofthe cladding layer 10 is larger to some extent.

Further, also with a view point of a manufacturing technique, a portionwithin a predetermined range from the edge portion 9 e is preferablyformed of the cladding layer 10. T-dies for molding a resin sheet oflarge width include those of long size having a longitudinal width ofthree meters or more. In the case of such layer size, bending maypossibly occur to some extent in the material for the die members 3, 4even by laser build-up welding that can be applied at a low strain. Oncebending occurs in the direction of the thickness of the die member, suchbending is rather difficult to repair. When the cladding layer width W2on the side of the lip end face is set somewhat larger, even whenbending occurs in the direction of the thickness of the die member, thelip portion 9 can be fabricated into a linear form by grinding. Sincebending less occurs in the direction of the height of the die membercompared with the bending in the direction of the thickness of the diemember, the cladding layer width W1 on the side of the lip mating facemay be smaller than the cladding layer width W2 on the side of the lipend face.

When each of the cladding layer width W1 on the side of the lip matingface and the cladding layer width W2 on the side of the lip end face ofthe cladding layer 10 is less than 0.2 mm, since the cladding layer 10is formed as an edge shape and plating film of good quality cannot beobtained in the plating process applied subsequently to cause a defectsuch as peeling and chipping at the boundary between the cladding layerand the chromium plating, which is not preferred. Then, with this pointof view, the cladding layer widths W1, W2 are preferably 0.2 mm or more.

Further, it has been known that when the diameter of the laser light is2.4 mm upon laser build-up welding, cracking or blow hole does not occurin the cladding layer and, in addition, cladding can be performed at ahigh efficiency. For performing the build-up welding efficiently by alaser of a light diameter of 2.4 mm (welding is performed by one passwith no weaving), the width of the build-up welding surface (inclinedsurface 4 a shown in FIG. 3) is preferably equal to or slightly largerthan 2.4 mm. As the cladding layer widths W1, W2 satisfying thecondition, a combination of W1=1.7 mm and W2=1.7 mm can be adopted.Further, when the cladding layer width W1 on the side of the lip matingface is set to a minimum value of 0.2 mm, the cladding layer width W2 onthe side of the lip end face can be set to 2.4 mm at the maximum.

In view of the above, it can be concluded that the cladding layer widthW1 is preferably 0.2 to 1.7 mm and the cladding layer width W2 ispreferably 0.2 to 2.4 mm. To be precise, a preferred value for thecladding layer width W1, W2 in the final product of the T-die 1 is avalue obtained by subtracting the thickness of the plating layer 20 fromthe preferred value of the cladding layer widths W1, W2. However, sincethe thickness of the plating layer in the final product is several tensμm, which is rather smaller than that of the cladding layer width W1,W2, this is neglected herein for the sake of explanation.

The radius R of the edge portion 9 a of the lip portion 9 (refer to FIG.1( b)), that is, the edge R is preferably 1 to 10 μm. In a resin filmmanufactured by an extruder using a T-die, it has been known that as theedge R is smaller, deviation of thickness, streak defect (die line), andresin stagnation are mitigated more. Accordingly, edge R of 10 μm orless is one of the standards for “sharp edge” in the industry. However,in the die members 3, 4 manufactured by the following method using thematerial described above, if the edge R is less than 1 μm, this is noteconomical since chipping is caused to the edge portion more frequentlyduring manufacture, upon attachment or detachment before and after use,during cleaning, and the like. With the reason described above, the edgeR is preferably 1 to 10 μm and, more preferably, 1 to 2 μm particularly.

As the material for the die members 3, 4, it is preferred to use a steelmaterial having a coefficient of thermal expansion close to that of thenickel-based alloy or cobalt-based alloy formed by laser build-upwelding of the alloy powder described above. Since powder laser build-upwelding gives less heat effect on the base material, inexpensivestructural alloy steels of low heat resistance, for example, SCM 420-SCM435 may be used as the base material with no problems. By using suchinexpensive structural alloy steels, the advantage of the hard chromiumplating can be provided effectively. Naturally, the kind of the steel asthe base material can be changed in accordance with the necessity and,for example, martensitic stainless steels excellent in corrosionresistance and hardness, specifically, SUS 420J2 or steels of similarkind can also be used, although the cost is increased. The coefficientof thermal expansion of the Ni-based alloy and the Co-based alloy isgenerally 10.5 to 12.5×10⁻⁶/° C., which is preferred also with a viewpoint that this is close to the coefficient of thermal expansion of thestructural alloy steels and the martensitic stainless steels describedabove.

Then, a method of manufacturing the die members 3, 4 of the T-die 1 isdescribed for an example of the die member 4 with reference to FIG. 3.

First, a material 4A for a die member 4 of a shape substantiallyidentical with that of a final shape (that is, larger than the finalshape by a working allowance) is provided (hereinafter referred to as“die material”). Then, as shown in FIG. 3( a), a vicinity of a portionof the die material 4A to form an edge portion of a lip portion 9 ischamfered (that is, a portion shown by a broken line is removed). Inthis case, a chamfering amount (dimension C1, C2) is preferably 4 mm orless. In this case, the width for the inclined surface 4 a is[(4)²+(4)²]^(1/2)=5.6 mm or less. When the cladding layer width W1 isset within a range of 0.2 to 1.7 mm and the cladding layer width W2 isset within a range of 0.2 to 2.4 mm as described above, the width forthe inclined surface 4 a is preferably within a range of[(0.2)²+(0.2)²]^(1/2) to [(1.7)²+(2.4)²]^(1/2), that is, from about 0.28mm to about 3 mm. However, the operability of the build-up welding maybe lowered if the width for the inclined surface 4 a is smaller than thelaser light diameter (spot diameter) where the laser light diameter is2.4 mm as described above. Thus, the width for the inclined surface 4 ais more preferably within a range of 2.4 mm to 3 mm.

Then, as shown in FIG. 3( b), a cladding layer 10 is piled up bycladding the nickel-based alloy powder (may also be cobalt-based alloypowder) by laser build-up welding over the inclined surface 4 a formedby chamfering. The laser build-up welding is to be describedspecifically later.

Then as shown in FIG. 3( c), the cladding layer 10 is partially removedby grinding such that the cladding layer 10 has a surface 10 b and asurface 10 c in flush with the lateral surface 4 b (lip mating face,that is, surface as an inner surface of a slit shape discharge portion8), and a lower surface 4 c (surface as a lip end face) of the diematerial 4A respectively. That is, a portion outside of a broken like ofthe cladding layer 10 shown in FIG. 3( b) is removed. As a result, aportion where the surface 10 b and the surface 10 c of the claddinglayer 10 intersect forms an edge 10 e (right angle edge). Duringgrinding, a portion of the die material 4A may be ground. Grinding fromthe state shown in FIG. 3( b) to the state shown in FIG. 3( c) may besaved. In this case, a state equivalent with the state shown in FIG. 3(f) can be attained by grinding the cladding layer 10 during grinding fortransferring the state shown in FIG. 3( e) to the state shown in FIG. 3(f) to be described later. However, in this case, since a relativelylarge amount of the cladding layer 10 has to be ground simultaneouslywith the plating layer 20 and this is not preferred with a view point ofworkability, it is desirable to perform a series of working steps shownin FIG. 3.

Then, as a pretreatment to hard chromium plating, under cutting isapplied for removing the lateral surface 4 b and the lower surface 4 crespectively so as to be lower than the surface 10 b and the surface 10c of the cladding layer 10 as shown in FIG. 3( d). In this case, aportion of the cladding layer 10 in contact with the die material 4A isalso removed together. That is, portions of the cladding layer 10 andthe die material 4A that are situated outside of the broken line shownin FIG. 3( c) are removed. The depth U1, U2 for under cutting isdetermined while considering the thickness of the plating layer 20 to beobtained finally. For example, the depth U1, U2 is set to a valuesubstantially equal with or slightly larger than the thickness of theplating layer 20 obtained finally.

Then, as shown in FIG. 3( e), hard chromium plating is applied over theentire surface of the die material 4A facing a molten resin flow channel5 (including the lateral surface 4 b), the cladding layer 10, and thelower surface 4 c of the die material 4 (surface as a lip end face),thereby forming a plating layer 20 comprising hard chromium. Thethickness of the plating layer 20 is set to a value sufficiently largerthan the final thickness, for example, about 100 μm since grinding is tobe applied subsequently. In application with hard chromium plating, anappropriate plating inhibition means (for example, masking) can beprovided to a portion not requiring plating. Alternatively, plating maybe removed from the portion not requiring plating by grinding or thelike after the plating.

Then, as shown in FIG. 3( f), grinding is performed such that the hardchromium plating layer 20 over the lateral surface 4 b and the lowersurface 4 c of the die material 4A are flush with the surfaces 10 b and10 c of the cladding layer 10 respectively. That is, portions outsidethe broken lines of the plating layer 20 shown in FIG. 3( e) areremoved. Grinding is further preceded slightly from the state and sharpedging is applied such that the edge R of the edge portion 10 e of thecladding layer 10 (the portion forms the edge portion 9 e of the lipportion 9) is from 1 to 2 μm. In this step, a portion of the surfaces 10b, 10 c of the cladding layer 10 is slightly ground. After the grindingdescribed above, polishing or lapping for mirror finishing may also beapplied. Since the cladding layer 10 formed by using the material asexemplified above has a good balance between the hardness and thetoughness and also has a small difference of hardness to the hardchromium plating layer 20, which is simultaneously in contact with theabrasive stone used for grinding the cladding layer 10, the edge portionof the lip portion can easily be sharp edged by grinding. It has beenconfirmed also that the edge portion 9 e having an edge R of 2 μm can befabricated in actual manufacture with no problem.

Further, the surface of the hard chromium plating of the die material 4Afacing the molten resin flow channel 5, particularly, the surface facingthe manifold portion and the hard chromium plating surface facing theslit shape discharge portion are preferably mirror finished by buffgrinding or the like.

After the series of processing for forming the cladding layer 10 and theplating layer 20, the entire die material 4A is fabricated into apredetermined final shape (by cutting, grinding, and mirror finishing),thereby completing manufacture of the die member 4. The die member 3 canbe manufactured also in the same manner. Since the thermal deformationof the entire die material 4A by laser build-up welding is extremelysmall, the working allowance provided to the die material 4A may beextremely small or, depending on the case, the laser build-up weldingand the plating can be performed also after the most portion of the diematerial 4A is fabricated into a predetermined final shape.

In the foregoing description, while it has been explained that each ofthe die members 3, 4 comprises a single piece, the die member cancomprise a plurality of pieces, for example, when forming a large-sizeddie member. For example, the die member can be configured also byforming a portion for a predetermined range (for example, a rangeincluding a lip mating face and a lip end face) from the lip portion 9as one piece (lip member having the cladding layer 10 and the platinglayer 20), and joining the lip member with other pieces by using bolts,etc.

Then, the laser build-up welding is to be described with reference toFIG. 4. FIG. 4 is an explanatory view showing an example of a laserbuild-up welding apparatus suitable to formation of the cladding layer10 described above. A laser light generated from a laser oscillator 101is applied by way of a mirror 102 and a condenser lens 103 onto aninclined surface 4 a of a die material 4A which is a base material to becladded. In this case, a focal point is controlled such that the focusof the irradiated laser light is not situated on the surface of the diematerial 4A (not focused on the surface of the base material A). Thelaser light diameter at the focal point can be, for example, about 2.4mm.

A pair of raw material powder supply nozzles 104 are attached beinginclined each at a predetermined angle to a portion intended forcladding over the die material 4A. A hopper 106 for storing the rawmaterial powder is provided in a raw material powder container 105, anda discharge amount of the raw material powder from the hopper 106 iscontrolled by a control disk 107. The raw material powder is preferablythe nickel-based alloy powder or the cobalt-based alloy powder asdescribed above. In view of the fluidity, a spherical atomized powder ismore preferred. The raw material powder discharged from the hopper 106is supplied from the raw material powder supply nozzle 104 together witha carrier gas comprising a non-reactive gas such as an inert gassupplied from a carrier gas supply source 108 to a portion intended forcladding. The raw material powder is melted by the energy of the laserlight and cladded over the die material 4A. In this step, a shield gascomprising a non-reactive gas such as an inert gas is supplied from ashield gas supply source 109 by way of a shield gas nozzle 110 to theperiphery of a portion intended for cladding. Accordingly, alarge-scaled equipment such as a vacuum chamber for housing the weldingdevice is not necessary. The die member 4A is held by a clamp 111. Byproviding a driving mechanism to the clamp 111 and moving the diematerial 4A in the direction perpendicular to the drawing, the claddingposition can be transferred. The cladding position may also be displacedby moving the laser build-up apparatus (optical system and nozzle).

Specific conditions of laser build-up welding are described below. Inparticular, for the material such as the nickel-based alloy powder orthe cobalt-based alloy powder incorporated with B (boron), which is hardand has high performance but which is liable to be cracked upon meltingand solidification, the laser irradiation intensity is preferablycontrolled such that the incident energy of the laser applied to thesurface of the base material is within a range of 30 to 150 J/mm². Ifthe incident energy is less than 30 J/mm², since the amount of heat isinsufficient, this tends to cause insufficient melting of the powder andinsufficient bonding with the base material. On the other hand, if theincident energy is more than 150 J/nrinre, the uppermost surface of thebase material is melted excessively, the constituent element of the basematerial, particularly, Fe (iron) diffuses extremely in the claddinglayer, by which the composition of the cladding layer is greatlydifferent from the composition of the metal powder failing to obtaindesired characteristics. Further, the degree of shrinkage uponsolidification increases by excess melting, tending to cause remarkablecracking.

Suitable build-up welding conditions include, for example, a laseroutput of 1300 W, a nozzle moving speed of 480 mm/min, and an incidentenergy of 86 J/mm². When a cladding layer was formed by using the (Nibased-1) alloy under the conditions, hardness near the edge portion ofthe cladding layer was 746 Hv and a hardness facilitating sharp edgingcould be obtained. A result in which the cladding layer is formed byusing the (Ni based-1) alloy within a range out of the preferredincident energy range of the laser is also described. When welding wasperformed under the conditions at the laser output of 800 W, the nozzlemoving speed of 240 nn/min, and the incident energy of 172 J/mm², the Fecontent in the cladding layer was more than 30%, that is, the claddinglayer comprised Fe (iron) as a main ingredient. In this case, thehardness was about 458 Hv and the cladding layer sometimes suffered fromcracking. Naturally, corrosion resistance can be neither expected withsuch a composition. Further, when welding was performed under theconditions at the laser output of 800 W, the nozzle moving speed of 1440nn/min, and the incident energy of 29 J/mm², many defects such asshrinkage cavity, blow hole, etc. occurred in the cladding layer and,further, melting and joining were insufficient, and the layer wasdetached from the base material during finishing.

According to the foregoing embodiment, the following excellent effectscan be obtained.

Since the laser build-up welding used for forming the cladding layer 10is performed by locally melting the metal by a laser light at a highenergy density, heat effect on the base material (die material) can bemitigated. Further, since the cladding width can be decreased by usingthe powdery shape material instead of rod-like, wire-like, orfiller-like material as the cladding material, the amount of heat inputto the base material is decreased and the surface of the base materialcan be cladded by the wear resistant metal with no undesired effect onthe base material.

Further, in the laser build-up welding, since the raw material powder issolidified by quenching after melting, the metallographic structureafter solidification is extremely fine and homogeneous. In the finemetallographic structure, hardness is also improved by Hall-Petch ruleand the like. In particular, in the Ni-based alloys-1 to 3 and theCo-based alloy-1, or alloys of compositions similar therewith, hardparticles such B compounds (metal borides) are precipitated, and thehard particles thereof are extremely fine as 0.1 μm or less and they areextremely homogeneous. FIG. 5 shows a copy of metallographic photographof a hard coating layer comprising the Ni-based alloy-1 formed by laserbuild-up welding (cladding layer 10). It is apparent also from thephotograph that a metallographic structure in which hard particles suchas fine metal borides (Mo boride, Ni—Mo boride, Ni boride, etc. in theexample of the photograph) are dispersed in a binder phase (in thisexample, a phase in which Mo and Si are solid solubilized in Ni) isformed. While the composition of the emerging hard particles changesdepending on the alloy ingredient, alloys used herein are in common inthat they contain at least one of metal boride and metal carbide as thehard particles.

Since the hard coat layer formed by laser build-up welding has anextremely fine and homogeneous structure, the layer suffers lessunevenness for the hardness caused by the dispersion state of hardparticles in comparison with that formed by HIP or flame spraying byusing the identical alloy. In HIP or flame spraying, since raw materialpowder is neither melted completely nor solidified by quenching, most ofthe hard particles have a particle diameter of 1 μm or more. It has beenrecognized generally that there is a difference in the hardness of 200Hv or more between a portion containing hard particles and a portion notcontaining them in the hard coat layer formed by HIP or flame spraying.On the contrary, since the metallographic structure formed by laserbuild-up welding is fine and homogeneous, variation of the hardness inthe hard coat layer is extremely small, which is confined within 40 Hv.FIG. 6A shows a hardness distribution in a hard coat layer formed bylaser build-up welding and FIG. 6B shows a hardness distribution in ahard coat layer formed by HIP, respectively. It is apparent that thehard coat layer formed by laser build-up welding shows less variation inhardness.

Further, since the metallographic structure formed by laser build-upwelding is fine and homogeneous, the surface roughness after finalfinishing such as polishing can be reduced extremely. Specifically, inthe Ni-based alloy-1 described above, the surface roughness of the hardcoat layer formed by laser build-up welding can be reduced to about 0.01Ra by lap finishing, whereas the surface roughness of the hard coatlayer formed by HIP can be reduced only to about 0.02 Ra. Also theNi-based alloys-2 to 3 and the Co-based alloy-1 described above show asimilar trend. Further, since the metallographic structure formed bylaser build-up welding is fine and homogeneous, the edge portion 9 e ofthe lip portion 9 can be finished to a sharp edge having an edge R at anorder of 1 to several μm.

Further, different from the HIP treatment (refer to the paragraph forthe background art), the laser build-up welding requires no extremelycomplicated preceding steps such as encapsulation for the periphery of asintered portion, filling of the capsule with the alloy powder, capsuledegassing and sealing, etc. Further, different from the HIP treatment,the laser build-up welding requires no large-scaled expensive equipmentcapable of providing a high temperature and a high pressure (forexample, 1300° C., 130 MPa) for the entire die material.

Further, different from the HIP treatment, the laser build-up weldingdoes not require to elevate the temperature of the entire die materialto the vicinity of the melting temperature of the alloy to be bonded.Besides, only the vicinity of the laser light irradiation portion islocally heated. Thus, bending of the die material (for example, iron andsteel material) is extremely small or negligibly small. This means thatfabrication of the die material in anticipation of thermal deformationis not necessary or can be minimized.

Further, as apparent from comparison with the HIP treatment describedabove, when compared with the hard coat layer (cladding layer) obtainedby flame splaying, the cladding layer 10 formed by the laser build-upwelding has advantages as follows: (1) more tough and free fromoccurrence of chipping, peeling, or cracking during grinding orpolishing; (2) free from lowering of the bonding strength or occurrenceof bonding defect at the boundary between the cladding layer 10 and thehard chromium plating layer 20; and (3) improved significantly in thesurface roughness of the lip portion 9 formed with the cladding layer10.

Further, since the cladding layer 10 formed by laser build-up weldingshows penetration to the die main body 3, 4 as the base material, thebonding strength with the base material is increased outstandingly whencompared with that of the cladding layer formed by flame spraying.

When damage such as chipping is caused at the lip portion 9,particularly, at the edge portion 9 e thereof, this can be repaired bygrinding the cladding layer 10 (also together with the hard chromiumplating layer 20) until the damage can no more be discriminated.Generally, in a case where a defect of 0.01 mm or more occurs, this isout of an allowable range and repairs will be made. The repairs can berepeated over and over until the cladding layer 10 and the hard chromiumlayer 20 formed initially are eliminated. The hard chromium platinglayer 20 can be restored at a reduced cost by a reverse electrifyingtreatment (plating peeling treatment) and a re-plating treatment.

When a relatively large defect occurs in the lip portion 9 and, if thesize of the defect does not exceed the width W1, W2 of the claddinglayer 10, the defect can be filled by the laser build-up welding. Thedefect can be repaired locally and instantaneously by changing thediameter of the laser light by changing the focal position of the laser.Since the repaired portion is piled up, grinding is applied such thatthe repaired portion is flush with the peripheral portion. Even when thedefect is repaired by laser build-up welding, the thermal effect remainslocal. Accordingly, the chromium plating layer 20 at the peripheryundergoes no undesired effect, thus the defect can be repaired to astate identical with that of a new product without peeling of plating orre-plating. Further, the die members 3, 4 are not distorted by the heateffect during repairs. That is, the repairing period is short and thequality of the die member after repairs is also satisfactory. Further,since such a large defect as exceeding the width W2 of the claddinglayer 10 (2.4 mm at the maximum in the case of the embodiment describedabove) scarcely occurs, the defect can be coped with by any of therepairing methods described above.

In the embodiment described above, while the T-die was used forextruding the molten resin, it may be used for discharging a coatingsolution.

DESCRIPTION OF REFERENCE CHARACTERS

-   1: T-die-   2: Die main body-   3, 4: Die member-   4A: Material, base material (die material)-   4 a: Third surface (inclined surface)-   4 b: First surface (surface as lip mating face)-   4 c: Second surface (surface as lip end face)-   5: (Fluid material flow channel) molted resin flow channel-   8: Discharge port-   9: Lip portion-   9 e: Edge portion of lip portion-   10: Cladding layer-   10 b, 10 c: Surface of cladding layer-   10: Edge portion of cladding layer-   20: Plating layer

1. A T-die comprising a die main body, the die main body being providedtherein with a fluid material flow channel, and the die main body havinga lip portion that forms a slit-shaped discharge portion at a tip end ofthe fluid material flow channel, wherein the lip portion includes acladding layer formed at least an edge portion thereof, the claddinglayer being formed by laser build-up welding to a base material with apowder of a corrosion resistant and wear resistant alloy comprising anickel-based alloy or a cobalt-based alloy.
 2. The T-die according toclaim 1, wherein a plating layer is provided on an inner wall surface ofthe fluid material flow channel in continuity with the cladding layer.3. The T-die according to claim 1, wherein the cladding layer has ametallographic structure in which a metal borides or a metal carbidesare dispersed in a binder phase.
 4. The T-die according to claim 1,wherein the cladding layer is formed to extend at a first width within arange of 0.2 to 1.7 mm from the edge of the lip portion along a lipmating face, and extend at a second width within a range of 0.2 to 2.4mm from the edge of the lip portion along a lip end face.
 5. Anextrusion molding machine having the T-die according to claim
 1. 6. Amethod of manufacturing the T-die according to claim 2, the methodincluding: a step of providing a material having a first surface that isa lip mating face, a second surface that is a lip end face, and a thirdsurface that connects the first surface and the second surface and isinclined thereto; a step of forming a cladding layer by laser build-upwelding over the third surface with a powder of a corrosion resistantand wear resistant alloy; a step of subsequently grinding the firstsurface and the second surface of the material together with portions ofthe cladding layer adjacent to the first surface and the second surface;a step of subsequently forming a plating layer over the surface of thecladding layer and over the first surface of the material; and a step ofsubsequently grinding the plating layer such that the cladding layer isexposed and the cladding layer has a surface flush with the surface ofthe plating layer lying over the first surface of the material.
 7. Themethod according to claim 6, wherein the width of the third surface isnot smaller than 0.28 mm but not larger than 3 mm.
 8. The T-dieaccording to claim 2, wherein the cladding layer has a metallographicstructure in which a metal borides or a metal carbides are dispersed ina binder phase.
 9. The T-die according to claim 2, wherein the claddinglayer is formed to extend at a first width within a range of 0.2 to 1.7mm from the edge of the lip portion along a lip mating face, and extendat a second width within a range of 0.2 to 2.4 mm from the edge of thelip portion along a lip end face.
 10. The T-die according to claim 3,wherein the cladding layer is formed to extend at a first width within arange of 0.2 to 1.7 mm from the edge of the lip portion along a lipmating face, and extend at a second width within a range of 0.2 to 2.4mm from the edge of the lip portion along a lip end face.